1. Field of the Invention
The present invention relates to image processing and more particularly to methods for processing of graphics image data which leads to improved compression, coding efficiency and resolution.
2. Description of the Prior Art
In the prior art there are many image processing systems. The following are systems representative of the prior art.
A paper by Spencer and Huang, presented at the Symposium on Computer Processing in Communications, Apr. 8-10, 1969, addresses the problem of transforming a gray scale image to an equivalent set of black/white images called bit planes. The paper does not show any method for modifying edge pixel values to improve compression.
U.S. Pat. No. 4,532,651 (Ser. No. 429,658) describes a filter for gray scale image data which forces the least significant bit of a current pixel equal to the most significant bit of the current pixel in a two bit per pixel representation when the most significant bit of a current pixel is equal to the most significant bit of a previous and a next pixel on the current scan line of an image. The method of this patent employs horizontal redundancy to filter all changes in second bit plane except for pixels adjacent to Black/White or White/Black changes in gray scale pixel values along a scan line. The patent does not shown any method for modifying edge pixel values of a graphics image to improve compression.
U.S. Pat. No. 4,532,503, (Ser. No. 440,114) describes a system which converts four level pixel intensity values to a sequence of three bilevel intensity values for each pixel in an image according to intensity values of neighbor pixels to increase display addressability and image resolution. The patent does not show a method for selectively modifying intermediate pixel values at edges in a graphics image to improve compression.
U.S. Pat. No. 4,546,385 (Ser. No. 509,837) describes data compression apparatus and method for separating a graphics image into at least first and second bit planes, identifying edge pixels from the first bit plane indicating a black/white change, locating the edge pixels and generating a single bit for each edge pixel indicating whether the edge pixel has a maximum intensity value such as black or white or an intermediate gray intensity value. Although the patent identifies edge pixels in an image, the patent does not show any method for modifying edge pixel values to improve compression.
An article in the IBM Technical Disclosure Bulletin, Vol. 22, No. 7, December 1979, at page 2980 and following shows a method for coding gray scale image data employing a vertical redundancy scheme. The publication shows a method for coding pixel values for gray level runs of pixels along a line by comparing the value on the current line to the value on the line above in the image. The article does not show a method for modifying edge pixel values in a graphics image to improve compression.
U.S. Pat. No. 4,006,298 generally discloses a system having an image gray scale using 64 discrete levels of brightness. The patent does not show a method for modifying edge pixel values in a graphics image to improve compression.
U.S. Pat. No. 4,177,470 shows a system wherein a binary data signal is operated on to reduce the number of bits in the signal without reducing information content of the signal. The patent shows basically a data compression system. The patent does not show a method for modifying edge pixel values in a graphics image to improve compression.
U.S. Pat. No. 4,210,936 shows a method and apparatus which achieves compression of image data by a reduction matrix which utilizes less gray scale data than is generated from the original picture element matrix. For example, if a picture element gray level required four bits of data, then the reproduction of the gray scale requires only one bit of data per pixel. The patent does not show a method for selectively modifying edge pixel values in a graphics image to improve compression.
U.S. Pat. No. 4,229,768 teaches an apparatus which compresses binary image signals by a selective run length compression technique. The patent does not show a method for modifying edge pixel values in a graphics image to improve compression.
U.S. Pat. No. 4,280,144 discloses apparatus and method for improving quality of a coarse scan, fine print image processing system. An encoder assigns a code to a coarsely scanned picture element representative of the reflectance characteristic thereof. For fine reproduction of coarsely scanned data, the coarsely scanned picture element is summed with at least four adjacent horizontal and vertical picture elements to reproduce a fine picture element comprising at least four sub-elements. Although the patent obtains information for determining a fine value of a particular picture element from adjacent picture elements, the patent in effect teaches a method for expanding data from a coarse scan to a fine representation. The patent does not show a method for modifying edge pixel values in a graphics image to improve compression.
The prior art discussed above does not teach nor suggest the present invention as disclosed and claimed herein.